Method of activating catalytic surfaces



Patented Jan. 27, 1942 2,270,874 METHOD OF ACTIVATING CATALYTIC SURFACESMarion H. Gwynn, Leonia, N. J.

No Drawing.

Application November 12, 1938,

Serial No. 240,007

7 Claims. (Cl. 252-240) This invention is a continuation in part ofpending application Serial Number 86,741, filed June 23, 1936, andentitled Methods of preparin and activating catalytic surfaces.

This invention relates to heterogeneous cata lysts and to thepreparation and reactivation of active metallic type catalytic surfaces,particularly those of compact surface and adherent or fixed to theunderlying metal. These activated surfaces are especially adapted foruse in sulphur ple in the formation of metallic sulphides; or asadsorption or purifying agents, as in the treatment of vegetable oranimal glycerides before steam deodorization, or as when doctorsweetening light petroleum or like distillates, or as tower packing orotherwise.

The essential part of this invention comprises distributing the vapor ofnitric acid to the various portions of a metal surface, such as nickel,said vapor attacking the surface to form a nitrate of the catalyticmetal. An example of means of distributing the vapor of nitric acid ismixing the vapor with a current of air. Other means of distributing andother purposes subsequently will become apparent. After sufficient vapornitration, the vapor is withdrawn and the catalytic metal nitrate isdecomposed, preferably in a current of air and preferably to a blackoxide. Without reduction in hydrogen or further chemical treatment, thesurface is then sufllciently active for use in hydroflning. Surfacesspent in hydroflning may be reactivated by means sub-,

stantially comprising the activation means, particularly maintaining thecatalytic metal nitrate coat compact or liquid during or upon vapornitrating.

Accessory treatments may be used prior to the vapor nitrating stepand/or after the nitrate decomposing step, e. g. as shown in the parentapplication Serial Number 86,741. If the catalytic surface issubstantially sulphided during hydroflning or use, the sulphur ispreferably removed prior to vapor nitrating. e. g. by roasting, whichmay be accompanied by steam or superheated steam treatment, or by anodicperoxidation in an aqueous electrolyte of lime or strontia or baryta, orby said roasting followed by peroxidation. Or water washing may beemployed prior to vapor nitrating or after nitrate decomposition.

Nitric acid has been previously used for catalyst activation, butgenerallyin liquid form, and generally to be followed by reduction inhydrogen after nitrate decomposition and prior to hydrogenation. The useof liquid nitric acid generally results in substantial losses of thecatalytic metal and insufficient and undistributed nitration ofsubstantial portions of the surface. Much of the nitrate coatingresulting from liquid nitric acid treatment is usually incompact. Whenpreviously disclosed in the vapor form, means of distributing the nitricacid vapors throughout the various portions of the surface have not beenused, and reduction in hydrogen prior to use appears to have beennecessary. The catalysis effected with such a catalyst would not beuniform, particularly with respect to the rate of catalyst degradation.

Distributing the nitric acid vapor effects subsequent uniform catalysisand minimizes or prevents refluxing off of the catalytic surface by thenitric acid. On reactivation, distributing insures the reactivation ofall portions of the catalyst surface or assembly, preventing subsequentpremature degradation of the whole by an unnitrated and contaminatedportion. Distributing is preferably obtained by a continuous feed orcurrent of vapor as by imparting volume increase and/or motion to theacid vapors, e. g. diluting as with air and/or applying differentialpressures. Distributing is aided by applying nitric acid vapor in excessof that combined on the surface. Distributing is aided by maintainingthe nitrate coating compact during the vapor nitrating. Distributing ispreferably also obtained by limiting the size or shape of the catalystmass or assembly, as will be described. Uniform temperatures throughoutthe various portions of the surface are useful in indicating orobtaining distribution.

The preferred form of this invention comprises distributing an excess ofthe vapor of heated or boiling nitric acid in a continuous current tothe various portions of the surface, and continuing to distribute anexcess of the vapor until the various portions of said surface arecompactly coated with catalytic metal hydrated nitrate to an averagedepth of at least 10 or 10 but less than about 10 atoms of the catalyticmetal; then gently heating to decompose said coating of nitrate to anoxide of the catalytic metal, preferably in a stream of air. The surfaceis catalytic without further treatment-and maintains a slow and uniformdegradation rate during catalysis.

The contacting vapor of nitric acid ornitric acid air mixture ispreferably supersaturated, as may be obtained by slightly chilling orcondensing the vapor before introducing to the various portions of thecatalytic surface, avoiding superheated vapor, particularly during theearly stages of nitration.

The common sulphur sensitive hydrogenating or hydrofining 'catalyticmetals may be activated by this invention, e. g. copper or nickel orcobalt. A mixture of these with others of the group or other metals may,also be reactivated, particularly if the nitrate layer yields a blackoxide on gentle roasting. A metal mixture maybe used which is similar tonickel and cobalt in the color of the gently decomposed oxide and in thecatalytic properties of that oxide, preferably also in ductility andferromagnetism as bulk metal. Palladium may also be reactivated by thisinvention.

The catalyst support is preferably the catalytic metal itself, althoughin bulk or noncatalytic form. However, other supports may be used, e. g.unglazed porcelain or alumina in a porous and granular form. Theunglazed porcelain or alumina may be impregnated with molten hydratednickel nitrate, the nitrate may then. be decomposed, the catalyst may besubsequently used and then reactivated as described herein.

An assembly for this invention may be made by electroplating a catalyticmetal upon a less noble or less catalytic metal, preferably assemblingand then heavily electroplating. -The electroplating is preferably at arelatively high current density and concentration of electrolyte. Anexample of a nickel plating bath is a strong ironfree aqueous solutionof nickel sulphate, together with sufllcient minor quantities of boricacid and nickel chloride or ammonium chloride to maintain a uniformdissolution of the nickel anode. The nickel is preferably plated on acopper assembly.

The invention is not confined to theories expressed herein, nor to thefollowing examples:

Example 1 The vapor nitrating vessel comprises an acid resisting closedand jacketed cylindrical vessel for containing liquid nitric acid at thebottom and the catalyst above, with a free space between the acid andcatalyst. The nitrating vessel also contains means of introducing astream of air into the liquid acid. The jacket may be partially filledwith water to surround the bottom and the lower portion of the sides ofthe nitrating vessel. Direct heat or steam may be applied to the waterto heat it. The upper portion of the jacket may have a vented trap toregulate the pressure and release the air of the resulting steam fromthe jacket.

The nickel catalyst to be vapor nitrated is assembled in a cylindricalscreen cage 2 inches in diameter and 36 inches in length. This is filledwith 4% pounds of clean nickel turnings whose average cross-sectionalarea is about 0.0002 square inch, and whose average thickness is 0.016inch. The superficial area of the turnings is about 3,500 square inches,the facial area of assembly is substantially that of the screen, viz.36x2 pi=226 square inches, and the. ratio thereof termed the surfaceratio is 15.5. The surface ratio of an otherwise similar cage but 3inches in diameter is 55 greater. In this invention, the surface ratiois preferably maintained at a value less than about 80, e. g. between 15or 20 and 30 or 40.

To vapor nitrate the cage, the latter is inserted and the heat is turnedon. A gentle stream of air is then passed through the aforesaid means ofintroducing air and subsequently the liquid acid is run into the vessel.The acid vapor air mixture moves up, around and into contact with thecage contents. The excess acid passing out above the cage may berecirculated or recovered from the air and returned to the bottom of thenitrating vessel. The air in the vapor mixture may be regulated todistribute the acid over the surface as may be determined by visualinspection or by the constancy of various catalyst temperature readingsor by a subsequent test. For example, small samples of turnings may beremoved from various portions of the cage, an equal weight of eachsample may be immersed in aqueous ammonium hydroxide to dissolve thenitrate, and

the color of the various solutions may then be compared. The nitrationis continued until the surface is coated with a layer of nickel nitrateat least l0 or 10 but averaging less than about 10 nickel atoms deep, e.g. until the net weight increase is between /4 and '/2 pound.

After discontinuing the nitration, the cage may be cooled, stored orshipped dry, or may then be gently roasted at near about the lowesttemperatures required to decompose the nitrate, e. g.

at near about 300 C. in a current of air until the brown fuming ceases.A relatively short contact or time at higher temperatures may be used.

The resulting nickel oxide is black and is generally catalytic withoutfurther treatment.

A cobalt or a cobalt and nickel surface may also be treated as in thisexample.

The vapor nitrated and gently roasted catalyst may be used in sulphursensitive hydroflning and may then be reactivated in a similar manner.Preferably the nickel nitrate is maintained in a compact form during thevapor nitration. For example, the nitrate coating is maintained in aliquid or viscous state as by moistening the air previous to contactwith nitric acid or by continuously or discontinuously diluting theliquid acid to a concentration slightly more aqueous than the constantboiling mixture. The aqueous content of the nitrate coat may forinstance be more hydrous than the dihydrate of nickel nitrate, aboutcorresponding to the trihydrate, for example. The extent of the vapornitration is preferably maintained nearly constant or uniform onsuccessive reactivations.

During the next step or immediately subsequent to vapor nitrating, thetemperature may be raised to about the temperatures where both incipientnitrate decomposition and nitric acid synthesis from the oxidation ofnitrogen oxides occur. The pressure also may be raised. Maintainingnitric acid synthesizing conditions on an oxide surface duringreactivation by vapor nitration, or other conditions which darken orenrich the blackness of the color of the subsequently decomposedcatalytic metal nitrate, may lessen the requirement of applied nitricacid. This or subsequent decomposing or roasting of the catalytic metalnitrate may more completely nitrate-or oxidize contaminants. Nitrogenoxides resulting from the decomposition step of the catalytic metalnitrate may be recovered and reused, e. g. by oxidation and absorption,to reform nitric acid.

ExampleZ An assembly composed of 16 parallel nickel screens attachedtogether is vapor nitrated essentially through the two flat faces. Anumber of such assemblies may be spaced apart in parallel and vapornitrated in a modification of the vapor nitrating vessel in Example 1.For instance the vessel, which may consist of enamel lined stainlessiron, may be horizontal with the vapors circulating up and through thespace between each assembly. The diameter of the screen wire is about0.016 inch.(0.04 cm.) and adjacent parallel wires are 0.095 inch (0.24cm.) apart onx centers, the surface ratio being about 4.5. The timeofvapor nitrating under otherwise similar conditions would be less thanone half that in Example 1. Where many assemblies are nitrated in thesame vessel, a manifold distributor may be used to decrease the volumeof air used. After vapor nitrating, the nitrate coating may bedecomposed, preferably to the black oxide, e. g. as described in Example1.

Cobalt surfaces may be similarly reactivated.

Continuous vapor nitrating may be carried out in a modified vapornitrating vessel, preferably horizontal, moving the catalyst through thenitrating vessel on an acid resisting conveyor. The catalytic materialis preferably chilled to solidify the nitrate coating prior to dischargefrom the conveyor. Granular or impregnated catalyst may be thuscontinuously vapor nitrated, or as in Example 1 when caged. Thisassembly, whether caged or uncaged, is preferably limited to arelatively low value of the surface ratio, similar to or below thatshown in Example 2.

Nitric acid may be boiled in a separate vessel, and the vapors may beled from this vessel into the vapor'nitrating vessel containing thecatalytic surface.

The methods and constructions described herein may be used inconjunction with other treatments, particularly those described in thecopending applications of the applicant, or may be otherwise used.

The parent application Serial Number 86,741 describes the anodicperoxidation of a decomposed nitrate surface, after forming the nitrateby immersing the surface in the vapors of heated nitric acid. Thecatalytic metal is readily peroxidizing and desulphurizing. The anodicperoxidation aqueous electrolytic bath is of low activity coeflicient inwhose anolyte hydroxyl is the predominant anion, preferably containingthe hydroxide of a metal selected from the group which consists ofcalcium, strontium and barium, or from the group which consists oflithium, calcium, strontium and barium. These and the other electrolytesdescribed in the said copending application may be used before or aftervapor nitrating and decomposing of the nitrate. When using vapornitrating as described herein in conjunction with anodic peroxidation ina bath containing the hydroxide of a metal selected from the groupconsisting of calcium and strontium and barium, the surface ratio of theassembly is preferably maintained of a low value, c. g. rapid activationis obtained when said value is above unity but less than about 4 or 5.For example an activated assembly as described in Example 2, and thenspent in sulphur sensitive hydrofining, may be reactivated by a processcomprising anodic peroxidation with an aforesaid preferred electrolyteand subsequent vapor nitration and nitrate decomposition as describedherein. Water washing, then drying, is preferably employed after anodicperoxidation and before vapor nitrating.

Copending application Serial Number 117,515, now U. 8. Patent 2,191,464describes activating a catalytic metal surface with a highly alkalinehypobromite or hypochlorite solution after partially activating thesurface with the vapors of heated nitric acid to form the nitrate anddecomposing the nitrate to. an oxide of the catalytic metal by gentleroasting. The hypohalite treatments described in said copendingapplication may be used after the activation treatment heretoforedescribed in this invention.

While unnecessary to render catalytic, the decomposed oxide from thevapor nitrated surface may be reduced in hydrogen prior to catalysis, inorder to modify said catalysis. For example, prior reduction in hydrogenmay be used to inhibit subsequent catalytic reactions other than simplehydrogenation or dehydrogenation. When used for the hydrogenation ofglycerides as described in the applicants copending application SerialNumber 233,032, filed October 8, 1938, the vapor nitrated and gentlyroasted nickel catalyst is preferably reduced in hydrogen.

After hydrogenating and/or purifying fatty or like compounds,particularly those which are not readily nitrated, these compounds orimpurities may be extracted, as by refluxing with volatile hydrocarbons.Or more polar solvents such as dichlorethylene or acetone may be used,particularly for a final or complete extraction or when using thecatalyst as a purifying agent.

Hydrofining with the surfaces described herein may be carried out forexample as described in U. S. Patent 2,073,578 and the copendingapplication Serial Number 130,478 entitled Method of continuouslyhydrofining carbonaceous vapors with solid sulphur sensitive catalyticsurfaces, filed March 8, 1937 now U. S. Patent 2,174,510.Desulphurization of organic compounds or solutions by these catalysts ispreferably accompanied by hydrogenation particularly replacing thesulphur with hydrogen. For example, a sulphurous and light petroleumdistillate may be sulphur sensitive hydroflned, the spent catalyticsurface may subsequently be roasted to convert the sulphide of thecatalytic metal substantially to an oxide, the roasted surface may thenbe subjected to vapor nitrating as described, the nitrate may bedecomposed, and then without further chemical treatmentthe activatedsurface may be used for hydrofining at a temperature below said sulphideroasting temperatures and below the temperature at which substantialpyrolysis occurs with said distillate.

What is claimed is:

1. In a method of activating the catalytic properties of a porous massof comminuted metal having extended surfaces of a sulphur sensitivehydrofining metal the step of treating said metal by conveying a wetmixture of nitric acid vapors and a non poisoning gas to said metaluntil an even adherent coating of hydrated nitrate of said metal havinga substantially uniform depth of at least 10 metal nitrate atoms isformed.

2. A method as described in claim 1 in which the average depth of thenitrate coating is less properties of a porous mass oi comminuted metalhaving extended surfaces of a sulphur sensitive hydroflning metal, thesteps or treating said metal by conveying a wet mixture of nitric acidvapors and a non poisoning gas through the tree spaces of an assembledcatalytic layer at an elevated temperature such that nitric acidsubstantially but incompletely condenses upon the catalytic surfacesforming an adherent coating of hydrated nitrate of said metal having asubstantially uniform depth oi at least 10 metal nitrate atoms, andsubsequently further heating to decompose said metal nitrate to a metaloxide.

5. A method as described in claim 4 in which the sulphur sensitivehydroflning metal is nickel and in which the surface was previouslyactivated by coating with a strong aqueous nickel nitrate solutionfollowed by gentle heating to decompose said nickel nitrate to a blacknickel oxide.

6. In a method of activating the catalytic properties of a porous massof comminuted' metal having extended surfaces or a sulphur sensitivehydroflning metal the steps of treating said metal by conveying a wetmixture of nitric acid vapors and a non poisoning gas to said metaluntil an even adherent coating of hydrated nitrate of said metal havinga substantially uniform depth of at least 10 metal nitrate atoms isformed, then substantially decomposing the metal nitrate by heatingabove 200 0., and subsequently further activating the surface anodicallyin an aqueous electrolytic bath 0! low activity coemcient and in whoseanclyte droxyl is the predominant anion.

'I. A method as described in claim 6 in which the sulphur sensitivehydronning metal is supported on an electrical conducting base, and inwhich the electrolytic bath comprises the hydroxide or a metal selectedfrom the group which consists of calcium, strontium and barium.

MARION H. GWYNN.

